Solution is available. Will be posted after. Please don't just give the two numbers. Show how you arrived at your answer. This problem is an excerpt from a book titled, A Course in Triangular Numbers by Paul Chika Emekwulu. Thank you.

sort by best latest

Well, the n-th triangular number is the sum of the first n numbers. So obviously 2 such numbers are:

1+2+3+...+14 = 105

and

1+2+3+...+14+15 = 120

You can help the HubPages community highlight top quality content by ranking this answer up or down.

Thought I had the right answer till I saw your proof!